The present invention relates to a vacuum evaporating method and apparatus for vacuum evaporation of magnetic layers onto a moving flexible tape- or strip-shaped base material such as high molecular material to thereby form a magnetic recording medium.
The following materials are conventionally used to form magnetic recording layers on a non-magnetic base: magnetic oxide powder such as .gamma.-Fe.sub.2 O.sub.3 ; .gamma.-Fe.sub.2 O.sub.3 doped with Co; Fe.sub.3 O.sub.4 ; Fe.sub.3 O.sub.4 doped with Co; berthollide of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 ; berthollide doped with Co, CrO.sub.2 and the like or coating types of alloy magnetic powder, primarily Fe, Co, Ni and the like, which are dispersed in organic binder such as vinyl chloride-vinyl acetate copolymer; styrene-butadiene copolymer; epoxy resin; and polyurethane resin. The magnetic recording layers are dried after coating.
Recently, the demand for high density magnetic recording types has increased. At the same time, high magnetic metallic layers formed by methods of vacuum evaporating, sputtering, ion-plating or the like have been given great attention as so-called non-binder type magnetic recording mediums which do not require a binder. Efforts have been made to commercialize such a non-binder type recording medium. Among the methods proposed for evaporating non-binder types of recording mediums, an oblique vacuum evaporation method in which vapor beams of magnetic metal are obliquely projected onto a base material has been preferred because of its simplicity. A previously known apparatus for carrying out this method produces a layer having excellent magnetic characteristics.
According to the prior art oblique vacuum evaporating method, a high magnetic material or the like is first evaporated from a single evaporation source at a predetermined incidental angle or at an angle within a predetermined incidental angle range onto a tape-shaped base which is moved linearly or along a curved path formed by a conveying cylindrical cooling can. However, since the base surface is angled with respect to the evaporation source and since the final thickness of the vacuum-evaporated layer varies as the cosine of the angle by which the vapor beam deviates from a right angle with respect to the base surface, as the angle of incidence increases, the evaporation efficiency deteriorates remarkably. Furthermore, due to the geometric arrangement of the tape-shaped material and the evaporation source, as the angle of incidence increases, the distance between the base surface and the evaporation source must be increased which causes a degradation of the evaporation efficiency.